Showing papers on "Tridymite published in 1983"

The low temperature field of liquid immiscibility in the system K 2 O-Al 2 O 3 -FeO-SiO 2 with special reference to the join fayalite-leucite-silica

Abstract: The extent of the low temperature field of liquid immiscibility in the system K2O-FeO-Al2O3-SiO2 in the vicinity of the plane fayalite-leucite-silica has been experimentally determined. The combination of direct oxygen buffering with the use of a zirconia probe to monitor oxygen activity has allowed minimisation of K2O-loss in the experiments while oxygen activity appropriate to the iron-wustite buffer has been maintained. The four-phase assemblage, fayalite+tridymite+FeO-rich liquid+SiO2-rich liquid, isobaric univariant in the quaternary system, occurs over a very small temperature range at about 1,163° C on the iron-wustite buffer. Both liquids appear to be in a coprecipitation relationship with tridymite and fayalite although the relationships between the two liquids are more complicated. The distribution of elements between the two coexisting liquids shows an interesting concordance when plotted in a new way. The results make sense in terms of current knowledge about silicate liquid structure, including the (familiar) observation that K/Al in the SiO2-rich liquid is always greater than in the coexisting FeO-rich liquid.